Technical Field
The present disclosure relates to a microelectromechanical gyroscope for sensing angular rate and to a method of sensing angular rate.
Description of the Related Art
As is known, use of microelectromechanical systems (MEMS) is increasingly widespread in various sectors of technology and has yielded encouraging results especially in the production of inertial sensors, microintegrated gyroscopes, and electromechanical oscillators for a wide range of applications.
In particular, there exist various types of MEMS gyroscopes, which are distinguished by their rather complex electromechanical structure and by the operating mode, but are in any case based upon detection of Coriolis accelerations. In MEMS gyroscopes of this type, a mass is elastically constrained to a substrate or stator to be able to translate in a driving direction and a sensing direction that are mutually perpendicular. By a control device, the mass is set in oscillation at a controlled frequency and amplitude in the driving direction.
When the gyroscope turns about an axis perpendicular to the driving direction and to the sensing direction at an angular rate, on account of the motion in the driving direction, the mass is subject to a Coriolis force and moves in the sensing direction. The displacements of the mass in the sensing direction are determined both by the angular rate and by the velocity in the driving direction and may be transduced into electrical signals. For instance, the mass and the substrate may be capacitively coupled so that the capacitance depends upon the position of the mass with respect to the substrate. The displacements of the mass in the sensing direction may thus be detected in the form of electrical signals modulated in amplitude in a way proportional to the angular rate, with carrier at the frequency of oscillation of the driving mass. Use of a demodulator makes it possible to obtain the modulating signal thus to derive the instantaneous angular rate.
In many cases, however, the acceleration signal that carries information regarding the instantaneous angular rate also contains spurious components that are not determined by the Coriolis acceleration and thus present in the form of disturbance. Not infrequently, for example, the spurious components may depend upon constructional imperfections of the micromechanical part, due to the limits of precision and to the production process spread. Typically, the effective oscillatory motion of the driving mass, as a result of a defect in the elastic constraints provided between the mass and the substrate, may be misaligned with respect to the direction expected theoretically. This type of defect commonly causes a quadrature signal component, which adds to the useful signal due to rotation of the microstructure. Like the Coriolis force, in fact, the misalignment causes the mass to displace also in the sensing direction, instead of just in the driving direction, and produces a variation of the capacitance between the mass and the substrate.
Obviously, the consequences are a degraded signal-to-noise ratio and an altered dynamic of the read interface, at the expense of the signal to be read, to an extent that depends upon the degree of the defects.